242 HYDRATES IN AQUEOUS SOLUTION. 



of plate 22. After the brass tube C had been introduced into the glass tube, 

 the washer R,made of blotting paper, was slipped up over the outside of the 

 glass tube until it would not pass through the shoulder of this tube. Then 

 the group of parts thus far described was let down through the hole at the 

 upper end of the hollow brass cylinder E, as far as it could go, i. c., until the 

 washer R was tightly squeezed between the glass and brass surfaces. The 

 three screws were next pushed through their respective holes, and turned 

 until the quartz plate M was forced, liquid-tight, into the conical hole in 

 the glass tube, care being taken at the same time so to adjust the system as to 

 have the axis of rotation of the glass tube and quartz plate parallel to the 

 axis of the brass cylinder E. A thread of convenient pitch had been accu- 

 rately cut in the inner surface of this cylinder. The purpose of this thread, 

 as well as that of a fine line or groove which had been turned on the outside 

 of the cylinder in a plane at right angles to the axis of the same, will be 

 explained below. 



Whenever the cell had been entirely taken apart (and this was not often 

 necessary) the distance between the plane of the lower surface of the quartz 

 plate M and the plane of the lower end of the cylinder E had to be measured 

 and recorded, since this distance varied with the thickness of the two washers 

 and with the pressure exerted by the screws. The number expressing this 

 distance was one of several numbers which had to be known in order to adjust 

 the cell for a given depth. 



The thread at E was next fitted to the thread which had been accurately 

 cut to fit it on the outside of the brass cylinder I. Then the two cylinders 

 were screwed together until the distance between the fine cut around the 

 outside of E and a certain point of the upper plane surface of the flange at 

 the bottom of the cylinder I had the proper value. This distance was, of 

 course, measured along a generating line of the outer surface at E, and hence 

 perpendicular to the plane just located. The assemblage of parts explained 

 above formed a complete system in itself, and comprised all of parts (6) and 

 (c), using the notation of the remarks introductory to the more detailed dis- 

 cussion of the cell. The flange at the bottom of I was provided with three 

 large holes and two small ones, and all of them pierced it parallel to the axis 

 of the cylinder. The larger holes fitted closely over three pillars (H and 

 H), while the smaller ones corresponded to two little screws. The pillars 

 and screws were not in the plane of the diagram. The object of the pillars 

 and screws will be explained a little later. The cylinder I was also turned 

 so as to have a collar on its interior near the top. 



When the desired depth of absorbing liquid, tho basis of intensity of 

 color, etc., had been determined upon, the distance between the line around 

 E and the upper plane of the flange of I was found by the addition of three 

 numbers. One of these was a constant of the apparatus 1.34 cm. and the 



